I took a series of images of lunar eclipse, through a thin and varying
cloud however. Then I processed them as I learned to do. Even with the
cloud veil, they still show the luminance gradients well, see the file
http://amper.ped.muni.cz/light/luminance/lun_eclipse/photom.htm or its
directory.
Next time we can mutually calibrate our instruments with such a hemisferic
luminance standard!
cheers,
jenik